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RFC 0011: Allow Intrinsic Functions and Pseudo-Parameter References in DeletionPolicy and UpdateReplacePolicy RFC #74
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| # Allow Intrinsic Functions and Pseudo-Parameter References in `DeletionPolicy` and `UpdateReplacePolicy` Resource attributes | ||
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| * **Original Author(s):**: @mingujo | ||
| * **Tracking Issue**: [Tracking Issue](https://github.com/aws-cloudformation/cfn-language-discussion/issues/11) | ||
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| # Summary | ||
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| Use CloudFormation [intrinsic functions](https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/intrinsic-function-reference.html) and [Pseudo-Parameter references](https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/pseudo-parameter-reference.html) to dynamically determine a value for DeletionPolicy and UpdateReplacePolicy Resource attributes | ||
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| # Examples | ||
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| ### Use [Ref](https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/intrinsic-function-reference-ref.html) | ||
| ```json | ||
| { | ||
| "AWSTemplateFormatVersion" : "2010-09-09", | ||
| "Parameters": { | ||
| "DeletionPolicyParam": { | ||
| "Type": "String", | ||
| "AllowedValues": ["Delete", "Retain", "Snapshot"], | ||
| "Default": "Delete" | ||
| }, | ||
| "UpdateReplacePolicyParam": { | ||
| "Type": "String", | ||
| "AllowedValues": ["Delete", "Retain", "Snapshot"], | ||
| "Default": "Delete" | ||
| } | ||
| }, | ||
| "Resources": { | ||
| "Table": { | ||
| "Type": "AWS::DynamoDB::Table", | ||
| "Properties": { | ||
| "KeySchema": [ | ||
| { | ||
| "AttributeName" : "primaryKey", | ||
| "KeyType" : "HASH" | ||
| } | ||
| ] | ||
| }, | ||
| "DeletionPolicy": { "Ref": "DeletionPolicyParameter" }, | ||
| "UpdateReplacePolicy": { "Ref": "UpdateReplacePolicyParam" } | ||
| } | ||
| } | ||
| } | ||
| ``` | ||
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| ### Use [Conditions](https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/conditions-section-structure.html) and [Fn::If](https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/intrinsic-function-reference-conditions.html#intrinsic-function-reference-conditions-if) based on Parameters | ||
| ```json | ||
| { | ||
| "AWSTemplateFormatVersion" : "2010-09-09", | ||
| "Parameters": { | ||
| "Stage": { | ||
| "Type": "String", | ||
| "AllowedValues": ["Prod", "Staging", "Dev"] | ||
| } | ||
| }, | ||
| "Conditions": { | ||
| "IsProd" : {"Fn::Equals" : [{"Ref" : "Stage"}, "Prod"]} | ||
| }, | ||
| "Resources": { | ||
| "Table": { | ||
| "Type": "AWS::DynamoDB::Table", | ||
| "Properties": { | ||
| "KeySchema": [ | ||
| { | ||
| "AttributeName" : "primaryKey", | ||
| "KeyType" : "HASH" | ||
| } | ||
| ] | ||
| }, | ||
| "DeletionPolicy": { | ||
| "Fn::If": [ "IsProd", "Retain", "Delete" ] | ||
| }, | ||
| "UpdateReplacePolicy": { | ||
| "Fn::If": [ "IsProd", "Retain", "Delete" ] | ||
| } | ||
| } | ||
| } | ||
| } | ||
| ``` | ||
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| ### Use [Fn::FindInMap](https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/intrinsic-function-reference-findinmap.html) and `AWS::Region` Pseudo-Parameter | ||
| ```json | ||
| { | ||
| "AWSTemplateFormatVersion" : "2010-09-09", | ||
| "Parameters": { | ||
| "Stage": { | ||
| "Type": "String", | ||
| "AllowedValues": ["Prod", "Staging", "Dev"] | ||
| } | ||
| }, | ||
| "Mappings" : { | ||
| "RegionMap" : { | ||
| "us-east-1" : { | ||
| "DeletionPolicy": "Retain", | ||
| "UpdateReplacePolicy": "Retain" | ||
| }, | ||
| "us-west-1" : { | ||
| "DeletionPolicy": "Delete", | ||
| "UpdateReplacePolicy": "Delete" | ||
| }, | ||
| "eu-west-1" : { | ||
| "DeletionPolicy": "Retain", | ||
| "UpdateReplacePolicy": "Delete" | ||
| }, | ||
| "ap-southeast-1" : { | ||
| "DeletionPolicy": "Delete", | ||
| "UpdateReplacePolicy": "Delete" | ||
| } | ||
| } | ||
| }, | ||
| "Resources": { | ||
| "Bucket": { | ||
| "Type": "AWS::S3::Bucket", | ||
| "DeletionPolicy": { | ||
| "Fn::FindInMap" : [ | ||
| "RegionMap", | ||
| { "Ref" : "AWS::Region" }, | ||
| "DeletionPolicy" | ||
| ] | ||
| }, | ||
| "UpdateReplacePolicy": { | ||
| "Fn::FindInMap" : [ | ||
| "RegionMap", | ||
| { "Ref" : "AWS::Region" }, | ||
| "UpdateReplacePolicy" | ||
| ] | ||
| } | ||
| } | ||
| } | ||
| } | ||
| ``` | ||
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| # Motivation | ||
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| CloudFormation customers expect to use conditions and intrinsic functions as values for `DeletionPolicy` and `UpdateReplacePolicy` Resource attributes as they can do elsewhere in the template. | ||
| The main ask from our customers was to allow them to vary DeletionPolicy and UpdateReplacePolicy values based on development stage, which tends to be passed in as a parameter, e.g., allow resource deletion in Dev stages but not Prod. This RFC proposes to support not only such use case but also other intrinsic function usages and Pseudo-parameter references. | ||
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| * References | ||
| * https://github.com/aws-cloudformation/cfn-language-discussion/issues/58 (149 thumbs up) | ||
| * https://github.com/aws/aws-cli/issues/3825 | ||
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| # Details | ||
| * The following intrinsic functions will be supported. | ||
| * [Ref](https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/intrinsic-function-reference-ref.html) | ||
| * [Fn::FindInMap](https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/intrinsic-function-reference-findinmap.html) | ||
| * [Fn::If](https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/intrinsic-function-reference-conditions.html#intrinsic-function-reference-conditions-if) | ||
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| * The following Pseudo-Parameters will be supported | ||
| * `AWS::AccountId`, `AWS::Region`, `AWS::Partition` | ||
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| # Limitation | ||
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| **Note:** This limitation is due to underlying implementation constraints. In the fullness of time, this limitation should be removed. | ||
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| Does not support expressions containing references to *[Resource properties](https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-template-resource-type-ref.html)* or *certain pseudo parameters* | ||
| * Unsupported Pseudo-Parameters | ||
| * `AWS::StackId`, `AWS::StackName`, `AWS::NotificationArns`, `AWS::URLSuffix`, `AWS::NoValue` | ||
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| # FAQ | ||
| * How about other Resource attributes such as CreationPolicy, DependsOn, Metadata, UpdatePolicy? | ||
| * They are out of scope of this RFC. | ||
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| * Will this be supported by CFN Lint (linter check for CFN template)? | ||
| * The AWS CloudFormation Linter (cfn-lint) will be updated to validate function and Pseudo-parameter usages under Resource attributes. | ||
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| # Appendix | ||
| ## More examples | ||
| ### Use [Fn::FindInMap](https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/intrinsic-function-reference-findinmap.html) and `AWS::Partition` | ||
| ```json | ||
| { | ||
| "AWSTemplateFormatVersion" : "2010-09-09", | ||
| "Parameters": { | ||
| "Stage": { | ||
| "Type": "String", | ||
| "AllowedValues": ["Prod", "Staging", "Dev"] | ||
| } | ||
| }, | ||
| "Mappings" : { | ||
| "PartitionMap" : { | ||
| "aws" : { | ||
| "DeletionPolicy": "Retain", | ||
| "UpdateReplacePolicy": "Retain" | ||
| }, | ||
| "aws-cn" : { | ||
| "DeletionPolicy": "Delete", | ||
| "UpdateReplacePolicy": "Delete" | ||
| }, | ||
| "aws-us-gov" : { | ||
| "DeletionPolicy": "Retain", | ||
| "UpdateReplacePolicy": "Delete" | ||
| } | ||
| } | ||
| }, | ||
| "Resources": { | ||
| "Table": { | ||
| "Type": "AWS::DynamoDB::Table", | ||
| "Properties": { | ||
| "KeySchema": [ | ||
| { | ||
| "AttributeName" : "primaryKey", | ||
| "KeyType" : "HASH" | ||
| } | ||
| ] | ||
| }, | ||
| "DeletionPolicy": { | ||
| "Fn::FindInMap" : [ | ||
| "PartitionMap", | ||
| { "Ref" : "AWS::Partition" }, | ||
| "DeletionPolicy" | ||
| ] | ||
| }, | ||
| "UpdateReplacePolicy": { | ||
| "Fn::FindInMap" : [ | ||
| "PartitionMap", | ||
| { "Ref" : "AWS::Partition" }, | ||
| "UpdateReplacePolicy" | ||
| ] | ||
| } | ||
| } | ||
| } | ||
| } | ||
| ``` | ||
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| ### Use [Fn::FindInMap](https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/intrinsic-function-reference-findinmap.html) and `AWS::Region` Pseudo-Parameter in YAML | ||
| ```yaml | ||
| AWSTemplateFormatVersion: "2010-09-09" | ||
| Parameters: | ||
| Stage: | ||
| Type: String | ||
| AllowedValues: | ||
| - Prod | ||
| - Staging | ||
| - Dev | ||
| Mappings: | ||
| RegionMap: | ||
| us-east-1: | ||
| DeletionPolicy: Retain | ||
| UpdateReplacePolicy: Retain | ||
| us-west-1: | ||
| DeletionPolicy: Delete | ||
| UpdateReplacePolicy: Delete | ||
| eu-west-1: | ||
| DeletionPolicy: Retain | ||
| UpdateReplacePolicy: Delete | ||
| ap-northeast-1: | ||
| DeletionPolicy: Delete | ||
| UpdateReplacePolicy: Delete | ||
| Resources: | ||
| Bucket: | ||
| Type: "AWS::S3::Bucket" | ||
| DeletionPolicy: !FindInMap [RegionMap, !Ref "AWS::Region", DeletionPolicy] | ||
| UpdateReplacePolicy: !FindInMap [RegionMap, !Ref "AWS::Region", DeletionPolicy] | ||
| ``` | ||
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Why does it have this limitation?
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Thanks for the question. These are short-term limitations due to underlying implementation constraints. In the fullness of time, these limitations should be removed.